The B/H ratio is not constant for ________

Question

Examoogle · Accepted Answer

Ferromagnetic materials

Explanation: The B/H ratio represents the permeability of a material, denoted as $\mu = B/H$. For ferromagnetic materials, this ratio is non-linear and depends on the magnetic field intensity (H) due to the presence of magnetic domains, leading to the B-H hysteresis curve.

Working Principle: In ferromagnetic materials, individual magnetic domains align with an external field, creating non-linear magnetization. As H increases, the material reaches a state of saturation, causing the permeability $\mu = B/H$ to vary continuously until saturation is reached.

Key Formulas: $B = \mu H$ — Relation between flux density and field intensity; $\mu_r = \frac{\mu}{\mu_0}$ — Relative permeability

Key Points: Non-magnetic materials (vacuum/air) have a constant $\mu_r = 1$.; Ferromagnetic materials exhibit saturation, causing the B/H ratio to decrease at high field intensities.; The B/H relationship for ferromagnetic materials is represented by the non-linear magnetization curve.

Advantages: High permeability allows for efficient magnetic flux concentration; Essential for transformer cores and electric motors

Disadvantages: Presence of hysteresis loss due to non-linear path; Saturation limits the maximum flux density in design

Applications: Transformer cores; Electromagnets; Inductor cores

Additional Info: Diamagnetic and paramagnetic materials have a nearly constant $\mu_r$, typically very close to 1.. The B-H curve for ferromagnetic materials is characteristically S-shaped (sigmoid) until saturation.

Answer: C is correct — Ferromagnetic materials exhibit a non-linear B-H relationship due to domain orientation and magnetic saturation, making the B/H ratio variable.

Exam Tip: Remember that constant permeability is a trait of linear materials; ferromagnetic materials are intrinsically non-linear and are defined by their B-H curves.

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